49 トリテルペンの骨格転位反応に関する研究

概要

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1) Backbone rearrangement in the reverse direction from biogenesis Treatment of 3α,4α- and 3β,4β-epoxy-D:A-friedo-18β,19αH-lupanes (1 and 2) with BF_3・OEt_2 gave 12-en-3-ols (11 and 14), 18-en-3-ols (12 and 15), and 19-en-3-ols (13 and 16) together with 5-en-3-ols (5 and 10) and 5(10)-en-3-ols (6 and 9). Epoxidation of alnus-5-en-3β-yl acetate gave 5β,6β-epoxide (21) and a small amount of α-epoxide (20). On treatment with BF_3・OEt_2, 20 afforded 1(10),5-diene (24) and a mixture of Δ^<12>- and Δ^<18>-oleanene derivatives. From the 12-ene derivative, daturadiol (28) was prepared. Solvolysis of 3β-tetrahydropyranyloxybaccharan-18β-yl mesylate (35) afforded, after deprotection and acetylation, dammarane derivatives (38, 42-46). 2) Backbone rearrangement in biogenetic direction BF_3・OEt_2-catalyzed backbone rearrangement of 13β,18β-epoxybaccharan-3β-yl acetate (50) gave a complex mixture, in which the formation of D:C-friedobacchar-9(11)-ene derivative (59) and 17(18→13)abeo-baccharane derivative (54) was shown. The formation of 59 constitutes the first example of energetically unfavorable rearrangement of triterpenes involving a sequential shift of the 14α-Me, 8β-Me, and 9α-H to 13α-Me, 14β-Me, and 8α-H, respectively.
天然有機化合物討論会の論文
1983-09-15